It is proposed to develop and apply electron microscope methods for studying how interesting sequences are distributed on DNA and RNA molecules. Techniques for improving the discrimination between single strand and duplex regions in electron microscope spreads, and for attaching labels recognizable in the electron microscope to particular RNA and DNA molecules will be developed. Methods for enriching for DNA strands carrying a particular gene or other sequence of interest are proposed. It is proposed to study the overall distribution of structural gene and HnRNA transcripts on eukaryotic DNA molecules by electron microscopy. Methods are proposed for mapping specific structural genes, - 4S RNA genes, 5S RNA genes, globin genes, immunoglobulin genes - on eukaryotic DNA molecules.